Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless communication devices such as radio telephone handsets, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, digital cameras, digital recording devices, video gaming devices, video game consoles, and the like. Digital video devices implement video compression techniques, such as MPEG-2, MPEG-4, or H.264/MPEG-4,Part 10, Advanced Video Coding (AVC), to transmit and receive digital video more efficiently. Video compression techniques perform spatial and temporal prediction to reduce or remove redundancy inherent in video sequences.
Video compression generally includes spatial prediction and/or temporal prediction. In particular, intra-coding relies on spatial prediction to reduce or remove spatial redundancy between video blocks within a given coded unit, which may comprise a video frame, a slice of a video frame, or the like. In contrast, inter-coding relies on temporal prediction to reduce or remove temporal redundancy between video blocks of successive coded units of a video sequence. For intra-coding, a video encoder performs spatial prediction to compress data based on other data within the same coded unit. For inter-coding, the video encoder performs motion estimation and motion compensation to track the movement of matching video blocks of two or more adjacent coded units.
After spatial or temporal prediction, a residual block is generated by subtracting a prediction video block generated during the prediction process from the original video block that is being coded. The residual block is thus indicative of the differences between the predictive block and the current block being coded. The video encoder may apply transform, quantization and entropy coding processes to further reduce the bit rate associated with communication of the residual block. The transform techniques may change a set of pixel values into transform coefficients, which represent the energy of the pixel values in the frequency domain. Quantization is applied to the transform coefficients, and generally involves a process that limits the number of bits associated with any given coefficient. Prior to entropy encoding, the video encoder scans the quantized coefficient block into a one-dimensional vector of coefficients. The video encoder entropy encodes the vector of quantized transform coefficients to further compress the residual data.
A video decoder may perform inverse entropy coding operations to retrieve the coefficients. Inverse scanning may also be performed at the decoder to form two-dimensional blocks from received one-dimensional vectors of coefficients. The video decoder then inverse quantizes and inverse transforms the coefficients to obtain the reconstructed residual block. The video decoder then decodes a prediction video block based on prediction information and the motion information. The video decoder then adds the prediction video block to the corresponding residual block in order to generate the reconstructed video block and to generate a decoded sequence of video information.